The fatigue life of steel bridges can be extended by externally bonding carbon fiber–reinforced polymer (CFRP) patches to the damaged elements to arrest the crack propagation. In this paper, the influence of the patch pretension level, stiffness, and fiber orientation on the stress intensity factor levels are investigated. A three-dimensional finite-element model of the double-sided CFRP patch-strengthened specimen is used to study the fracture behavior of an inclined edge crack under different combinations of loading Modes I and II. The introduction of a compressive stress by pretensioning of the CFRP patch prior to bonding produced a significant reduction of up to 70% in stress intensity factors (SIFs) for different crack lengths, which led to increasing the remaining fatigue life of the steel member. The increase in the CFRP patch-to-steel axial stiffness ratio reduced the SIFs by up to 30%. The optimum benefit of using the CFRP patch to reduce mode I SIF was accomplished when the patch axial s...

Bonding a composite patch to a cracked steel section is an efficient technique to reinforce cracked members or to delay fatigue crack growth in the structural elements. In this paper, a numerical study was performed to highlight the effect of bonded prestressed composite patches on the fracture parameters, such as crack tip opening displacement and the plastic zone. A three-dimensional finite element model of the double sided strengthened specimen is used to study the fracture behavior of an inclined edge crack under different combinations of modes I and II loading conditions. The influence of the pretension level, patch stiffness ratio, and fiber orientation on the crack tip opening displacement and plastic zone are also investigated. The introduction of a compressive stress by pretensioning of the composite patch prior to bonding produces a significant reduction in the crack tip opening displacement and plastic zone. This pretensioning reduces the crack tip driving force and subsequently reduces...

Due to the complexity of composite material, numerical methods are generally utilized in their analysis and design. Commercial finite element (FE) codes, such as ANSYS and ABAQUS, allow the implementation of user subroutines in the program, which provides the advantage of using high meshing and solving technologies besides the improvement of materials and/or elements models. Nonlinearities arise for many engineering problems, for example, the progressive damage of a composite element that contains sources of stress concentration or damage localization such as holes, bolts, and/or flaws causes nonlinear material behavior. In order to simulate this nonlinear behavior, especially in 3D, an accurate material constitutive model is required. Therefore, the objective of this paper was to simulate the 3D progressive damage model of composite materials by using simple numerical models. In this paper, ANSYS user subroutine (USERMAT) was used to simulate the progressive damage behavior of a composite plate containing holes using simple models. Three different material models were used: ply discount model (PDM), simple progressive damage model (SPDM) by adding an empirical progressive damage criteria to the PDM, and continuum damage mechanics model (CDMM). Good agreements were observed between SPDM, CDMM, and published experimental results. Furthermore, CDMM showed the least dependence on mesh size. Three different damage evolution laws, linear, quadratic, and degradation laws, were adjusted and tested. It was found that there was no significant difference in the predicted failure load between these selected laws.

Unfortunately, fibrous composite materials' mixed-mode fracture toughness (K _eff ) was measured using inappropriate through-thickness cracked (TTC) specimens. The problem with such specimens is the ignorance of the fibers in the pre-notch surfaces, i.e., no fiber bridging behind the crack tip. In the present paper, a real K _eff of fiber-reinforced concrete (FRC) was experimentally determined using matrix cracked (MC) specimens. Traditional (TTC) specimens were also adopted for comparison. The effect of fiber length (35 mm, 50 mm, and hybrid fibers, 50% from each length) and mode of mixity (M ^e ), M ^e = 0, 1/4, and 1/2 were studied. Hooked end steel fibers of a volume fraction equal to 1% were used. All cracked beams with a crack-length-to-beam-depth ratio equal to 0.3 were tested under three-point bending in mode I and mixed-mode. The span/depth ratio was equal to two for all specimens. Since there is no equation to predict the K _eff of MC specimens and the inapplicability of Griffith's theory to predict the K _eff due to the difference in crack paths, new realistic procedures were suggested to overcome this dilemma. The results indicated that MC specimens recorded a lower crack initiation load than the peak load. In contrast, the crack initiation load coincides with the peak load in the case of TTC specimens. This reflected the role of steel fibers behind the crack tip in retarding the specimens to reach their ultimate capacity after crack initiation. K _eff increased with increasing M ^e . Although long fibers recorded higher peak load and energy, their effect on K _eff of MC FRC specimens was marginal due to the minor effect of fiber length on the crack initiation loads. The MC specimen is a realistic approach for estimating the K _eff of FRC.

Recent explosions and impact events have highlighted the exposure of civil structures, prompting the need for resilient new constructions and retrofitting of existing ones. Laminated glass panels, particularly in glazed facades, are increasingly used to enhance blast resistance. However, the understanding of glass fragments and their interaction with the interlayer is still incomplete. This paper investigates experimentally the quasi-static and dynamic responses of cured and uncured polymers for seven different materials—two different products of polyvinyl butyral (PVB), two ethylene vinyl acetate products (EVA), one product of thermoplastic polyurethane (TPU), and two SentryGlas products (SG)—that were tested between 21 and 32 °C (69.8 and 89.6 °F), which is the recommended room temperature. In these experiments, the responses of PVB, EVA, TPU, and SG were evaluated under a quasi-static strain rate of 0.033 s⁻¹ and compared to the results under a relatively higher strain rate of 2 s⁻¹. Moreover, the high strain rate loading of the materials was accomplished using a drop-weight testing appliance to evaluate the engineering stress–strain response under strain rates between 20 and 50 s⁻¹. The results demonstrated that with strain rates of 20 s⁻¹, PVB behaved like a material with viscoelastic characteristics, but at 45 s⁻¹ strain rates, PVB became a non-elastic material. SG, on the other hand, offered both a high stiffness and a high level of transparency, making it a very good alternative to PVB in structural applications. In contrast, after the maximum stress point, the response to the failure of the seven materials differed significantly. The tests provided ample information for evaluating alternative approaches to modeling these different materials in blast events.